The present invention relates to an electromagnetic injector for controlling the fuel quantity to be fed into an internal combustion engine.
Electromagnetic injectors are conventionally used in present-day gasoline and Diesel fuel injection systems. The conventional electromagnetic injectors use single-coil concepts. In this connection, a magnetic field is built up by having one coil traversed by current flow, thereby generating a magnetic flux in the surrounding magnetic circuit. A valve body is moved by the magnetic flux acting upon a movable magnet armature connected to the valve body via an air space. The opening duration of the electromagnetic injector and, thus, the injection quantity are controlled by varying the duration of current flow traversing the coil.
In principle, the buildup of magnetic flux in a magnetic circuit of a coil does not occur instantaneously in response to current flowing in the coil but occurs with a certain time delay. The time delay of the build-up of the field depends on many factors, such as the geometry of the magnetic circuit, and especially on field diffusion and the eddy currents, thus produced. Eddy currents are electrical currents induced in massive, electrically conductive bodies by a temporally variable magnetic field, such as during the buildup of the magnetic field. In the process, the eddy currents counteract a rapid field diffusion.
The time delay between current flow in the coil and field buildup leads to an undesired increase in the response time of electromagnetic injectors. Response times of 100 xcexcs or less, which are required in modern injection systems, are currently made possible only by higher voltages made possible with the aid of booster capacitors, or by costly switched double coil systems with mutually canceling force effect. The disadvantage with these conventional systems is the high constructive effort required for the electrical circuits, which goes along with high costs and great space requirements.
The electromagnetic injector according to the present invention offers the advantage of a short response time and low circuit cost. To accomplish this, the injector according to the present invention includes an electromagnetic coil system having at least two concentrically arranged coils, the coils being integrated into a magnetic circuit so that between two adjacent coils a first pole body is positioned in each case, and an inner and outer coil is in each case adjacent to a second pole body, the first and second pole bodies being components of the magnetic circuit of the electromagnetic coil system, and in each case adjacent coils having a common field current flow through them in directions opposite to each other. In such a multi-coil system, because of letting current flow in the coils in the opposite direction, in the inner-lying first pole body a mutually opposite field direction of the generated eddy currents occurs, and thus the eddy currents are extinguished. As a result, the field diffusion and thus the force buildup of the magnetic circuit occur considerably faster than in a conventional one-coil system. In addition, in the first pole body between two coils, the magnetic field is constructively magnified, since at this point the two magnetic fields overlap codirectionally, and thus a greater magnetic flux is generated.
According to one example embodiment of the injector according to the present invention, the pole bodies are dimensioned so that a radial cut surface of a middle first pole body is substantially equal to the sum of the cut surfaces of the two adjacent pole bodies. In the case of a geometry of a magnetic circuit selected in this manner, the mutual cancellation of actions of force of two adjacent coils is prevented.
The coils may have approximately identical characteristics, especially equal inductivity.
The coils may be arranged in a parallel circuit.
Advantageous further developments of the present invention result from the measures indicated in the dependent claims.